Karstbase Bibliography Database

Original article
Wagner, T.
Datierung fluviatiler höhlensedimente mittels kosmogener nuklide am beispiel des grazer berglandes
Dating of fluvial cave sediments using cosmogenic nuclides: a case study from the Grazer Bergland
2011
62
-3
3
14
The Central Styrian Karst north of Graz comprises a great number of caves of which many are of phreatic origin. Due to a clustering of caves at certain elevations above the current base level, the Mur River, these caves can be assigned to distinct levels. Caves cannot be older than the rock in which they formed, i.e. in the case of the region studied here not older than about 400 Ma (million years ago). Cave deposits on the other hand allow to infer a minimum age of cave formation, because they are deposited in the cave during or (mostly) after its development. Besides numerous autochthonous (i.e. in situ) sediments and speleothems, also a number of allochthonous (transported into the cave from the surface) sediments are encountered. Burial ages of several quartz-rich allochthonous cave sediments were determined using the radioactive cosmogenic nuclides 26Al and 10Be. The present article provides an insight into this rela tively new dating method (burial age dating) to constrain the age of cave deposits. The current state of knowledge about the timing of cave formation in the Grazer Bergland (Highland of Graz) will be discussed by summarizing the results of two recent papers (Wagner et al., 2010, 2011). Based on these results, conclusions are drawn about the age of the cave levels, relative incision rates of the River Mur and the landscape evolution of the eastern rim of the Alps in general. Sedimentation ages of 0 to about 5 Ma ago are in good agreement with increasingly higher cave levels above the present base level. This in turn reflects the stepwise relative incision of the River Mur. Based on the oldest samples, the onset of karstification and thus the exhumation of the Central Styrian Karst occurred at least 4-5 Ma ago. The oldest level, assigned to an age of at least 4 Ma, is situated some 500 m above the current valley bottom. Therefore, a relative incision rate of the River Mur in the order of only about 100 meters per million year (m/Myr) for the last 4-5 Ma is inferred. A more detailed examination of the levels reveals on average a decrease in the incision rate. Burial ages of ~2.5 Ma are determined only 100 m above the current base level. Moreover, the formation of planation surfaces and terraces in the Grazer Bergland is constrained by the correlation with cave levels and as such an important contribution to the understanding of landscape evolution of this region is made.